There are many medical conditions which require the administration of liquid medicaments transcutaneously (through the skin) for prolonged periods. Diabetes, for example, may be controlled by daily, or more frequent, injections of insulin.
Since transcutaneous injections are painful and troublesome, and since each injection represents a possibility for infection, injections are spaced at intervals as far apart as possible, resulting in peak and valley concentrations of the medicament in the bloodstream or at the site in the body requiring the medicament, the peak concentrations occurring shortly after the administration of the medicament and the low, or valley, concentrations occurring shortly before the administration of the next injection. This method of administration exposes the patient to the possibility of overdose at peak levels and underdose at valley levels, but was nevertheless the standard method for many years in the absence of a better alternative.
Recently, systems have been developed in which a catheter is semi-permanently implanted in a patient to provide access to a transcutaneous site in a patient's body, and a liquid medicament is supplied to the catheter from a reservoir.
Insigler and Kirtz (Diabetics, 28: 196-203, 1979) describe a portable insulin dosage regulating apparatus which uses an electrically driven mini-pump with an insulin reservoir to periodically dispense a predetermined number of insulin units (U). A small electronic control box is used to set the basal rate of 0.4 U/hr in stages of 0.2 U each. A switch is used to trigger a program that infuses a higher dose for a period of one hour, after which the system automatically goes back to the basal rate.
Thomas et al. U.S. Pat. No. 3,963,380, issued June 15, 1976, describes a novel micropump driven by piezoelectric disk benders. Although the pump draws only a small current, it requires a voltage of about 100 volts to drive the pump.
Tamborlane et al. (The New England Journal of Medicine, 300: 573-578, No. 11, Mar. 15, 1979) describe a portable subcutaneous insulin delivery system which uses a battery driven syringe pump. The apparatus is bulky and heavy.
A peristaltic motor driven pump has been described by Albisser et al. (Med. Progr. Technol. 5: 187-193 [1978]). The pump weighs 525 g. and consumes 60 milliwatts at maximum pumping rates. This system has a continuous duty cycle. It is bulky and heavy and consumes a relatively large amount of power.
It is an objective of the present invention to provide a simple light weight system for the transcutaneous infusion of a liquid medicament into a patient in controlled doses over an extended period.